1. Field of the Invention
The present invention relates to a cooling device for a battery pack including a plurality of prismatic rechargeable batteries that are arranged in parallel and to such a rechargeable battery.
2. Description of Related Art
In a conventional battery pack, in order to prevent decrease in a battery output, charging/discharging efficiency, and battery service life due to the elevation of the battery temperature by heat generation that occurs along with charging/discharging, for example, a fan is provided to send cooling air between cells in the battery pack or between battery modules, each including a plurality of serially connected cells.
The above-mentioned structure will be described with reference to FIGS. 8 and 9. In FIG. 8, reference numeral 31 denotes a battery pack serving as a power source for electric vehicles including hybrid cars. In the battery pack 31, twenty to thirty rechargeable batteries 32 are arranged in parallel with ventilation spaces 34 being provided between the respective rechargeable batteries 32. The batteries 32 are interposed between a pair of end plates 35 that are provided on both ends of the rechargeable batteries 32 so as to be integrally fixed therebetween, thereby constituting the battery pack 31. As shown in FIG. 9, each of the rechargeable batteries 32 is constituted as a battery module that is formed by arranging a plurality of cells 33 in parallel in an integrated manner and internally connecting the cells 33 in series. Each of the cells 33 is constituted by housing an electrode plate group 33b and an electrolyte solution in a battery case 33a. Connection terminals 36 provided on both sides of the rechargeable batteries 32 are connected in series so as to obtain a predetermined output voltage of the battery pack 31.
An air path 38 is provided in a support frame 37 for supporting the battery pack 31, whereas an air exhausting path 39 is provided above the battery pack 31. Reference numeral 40 denotes an air duct for taking air inside a vehicle compartment so as to provide cooling air through the air path 38. A blower fan 41 is provided in the middle of the air duct 40. Reference numeral 42 denotes a reflux duct for refluxing the cooling air exhausted from the air exhausting path 39 into the vehicle compartment.
Temperature detection sensors 43 are attached to the upper ends of the battery case 33a of appropriate cells 33 included in each of the rechargeable batteries 32. Detection signals from the temperature detection sensors 43 are input to a temperature detection section 44 so as to detect a temperature of each of the rechargeable batteries 32. Temperature data of each of the rechargeable batteries 32 is input to a control section 45 which in turn obtains a mean temperature of the rechargeable batteries 32. The amount of cooling air created by the blower fan 41 is controlled in accordance with the obtained mean temperature.
The attachment structure of each of the temperature detection sensors 43 is as follows. As shown in FIG. 9, a temperature detection hole 46, which is sealed from inside of the battery case 33a and is open to the exterior, is provided on the upper end of an appropriate cell 33. The temperature detection sensor 43 is inserted into the temperature detection hole 46 to be attached through an adhesive or a resin, thermally fused, or fixed, thereby allowing the detection of a temperature inside the cell from the exterior of the cell.
The above-described cooling device for the battery pack employs an upflow system for upwardly blowing cooling air from below the battery pack 31. The cooling is controlled by detecting a temperature of the cell with the temperature detection sensor 43 provided on the upper end of the rechargeable battery 32. However, since heat generating portions such as the connection terminals 36 and joint portions 33c between the cells 33 concentrate in the upper part of the rechargeable battery 32, this upper part has a high temperature as compared with its lower part or the like. Consequently, the upflow system is disadvantageous in that cooling efficiency is impaired because a portion having a higher temperature is cooled with cooling air having the lowered cooling capacity and that a variation in temperature between the upper part and the lower part of the rechargeable battery 32 is increased.
What is worse, in the upflow system, the air duct 46 or the like is required to be provided in a largely devious manner so as to take the air inside a vehicle compartment and to send it as shown in FIG. 8. As a result, the cost is adversely increased, and the space cannot be reduced due to the provision of the air duct 40.
In a case where a downflow system for allowing cooling air to downwardly flow from above the battery pack 31, a temperature of a portion of the cell having the highest temperature cannot be detected because the temperature detection sensors 43 are attached on the upper end of the rechargeable battery 32, that is the most cooled portion.